Creating Surface Flux Maps from Airborne Measurements: Application to the Mackenzie Area GEWEX Study MAGS 1999 |
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| Authors: | Matthias Mauder Raymond L Desjardins Ian MacPherson |
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| Institution: | (1) Agriculture and Agri-Food Canada Research Branch, 960 Carling Ave., Ottawa, ON, Canada, K1A0C6;(2) Flight Research Laboratory, Institute for Aerospace Research, National Research Council, Ottawa, ON, Canada |
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| Abstract: | The objective of this study is to produce two-dimensional maps of the sensible and the latent heat fluxes from airborne measurements,
based on the analysis of a flight pattern, called grid flights. A footprint model with along-wind and cross-wind components
was used to project the measured fluxes onto the surface map. The method was applied to measurements over Arctic tundra during
the Mackenzie Area GEWEX (Global Energy and Water Cycle Experiment) Study (MAGS) 1999. The resulting flux estimates were computed
by integration of a wavelet transform, and corrected for long wavelength losses using information from 100 km long regional
runs that were conducted close to the grid flights. The random flux error was estimated based on the flight length that is
represented in each map element, and a map resolution of 3 × 3 km was chosen in order to keep the average random error of
the latent heat flux below 25%. The random error of the sensible heat flux was smaller by a factor of 1.4 on average. An analysis
of airborne flux measurements at different altitudes showed no significant increase of flux estimates for measurement heights
below 90 m. Thus, the fluxes measured at heights between 48 and 64 m were not corrected for vertical flux divergence. The
resulting flux maps provide quantitative two-dimensional estimates of the energy exchange between the surface and the atmosphere
during the snow melt period in an Arctic environment, which are well-suited for calibration and validation of numerical models. |
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| Keywords: | Airborne flux measurements Flux mapping Footprint Random error Systematic error Vertical flux divergence |
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